Do you run bright lights? Like is this a tank you have bright lights or light on for a certain period of time? CPDS when they are tiny and shipped like this to the store are VERY VERY sick and malnourished. They haven't been fed well, (most given flake if anything), and will be VERY shocked from all the hustle and bustle. Take them out and put them in a Q tank with LOTS AND LOTS of plastic plants, like you cannot see them. Then feed them up, and deworm them. They have sunked in bellies don't they? That's because they are fed crap at the store. You need VERY low light, they are very shy and are being out competed for food, and the lights aren't helping. They need a low light tank, for the first couple weeks. To get used to you, it took me 2 months to convince the ones I have now to eat in front of me, and tolerate the light on. Once a month has past you should be clear, also they don't like a lot of flow in the beginning, once fed up and pretty then they like moderate flow in the tank.
Food to feed to help them adjust
Daphia
Decapped brine
Live Brine shrimp
Blood worms